www.paizo.com go to their downloads section. All (well most) old TSR D&D books are available as pdfs for $4 each. Plenty of Ravenloft stuff there. The campaign setting, monstrous compendiums with good descriptions, the various modules, etc. are in the 2e section of WotC portion of the downloads.
The original ravenloft module however is in the WotC section of Downloads, in the 1e section under Ravenloft.
WotC also has the second 1e ravenloft book as a free pdf download on their website.